Watercraft are often powered by an outboard motor positioned at a stern of the craft. The outboard motor has a powerhead and a water propulsion device, such as a propeller. The powerhead includes a cowling in which is positioned an internal combustion engine, the engine having an output shaft arranged to drive the water propulsion device.
Generally, the motor is connected to the watercraft in a manner which permits the motor to be "trimmed" up and down. For example, the motor may be connected through a horizontally extending pivot pin to a clamping bracket which attaches to the watercraft. In this manner, the motor may be moved in a vertical plane about the axis of the pin. This allows an operator of the watercraft to raise the propeller out of the water of place it deep in the water dependent upon the trim angle of the motor.
In addition, the motor is arranged to turn left and right about a generally vertically extending axis. This arrangement permits the operator of the watercraft to change the propulsion direction of the motor, and thus change the direction in which the watercraft is propelled.
The size of the motor, especially the powerhead portion which includes the motor, effects the air drag associated with the watercraft. It is desirable for the motor to have a small profile to reduce the air drag. In addition, it is generally desirable for the engine to be compact, since this makes the task of trimming and turning the motor less difficult.
The engine typically is of the internal combustion type with one or a plurality of cylinders. Internal combustion engines typically incorporate reciprocating piston in the cylinders. The engines typically operate on the two or four stroke principal. In either of the two or four stroke cycle there is a compression stage where the piston is compressing the fuel and air mixture within the cylinder before the ignition system is triggered. During this compression stroke some of the fuel and air mixture passes by the piston seal ring and then travels to the crankcase chamber.
As the engine operates more of the fuel and air mixture builds accumulates in crankcase which can cause a build up of pressure. This pressure build up can impede the movement of the piston and therefore degrade engine performance. It is well known to attach a breather mechanism to the crankcase which prevents the pressure build up in the crankcase of the engine. It is further well known to provided hose means to deliver the fuel air charge back to an intake portion of the engine.
There are several problems with this type of arrangement particularly when the engine is cool and has not properly warmed up. When the engine is cool the pistons are typically cool and the pistons as well as the corresponding piston seals have not expanded due to thermal expansion. This results in the seal between piston and the cylinder not being as effective as compared to when the engine is at a standard operation temperature. This lack of a proper seal causes more blow by gas to accumulate in the crankcase. Further, as this engine is a non-assisted aspirating engine the ability of the engine to draw air intake an intake system is diminished when the engine is cold.
This results in several problems with the typical delivery arrangement of blow-by gas to an intake member. First because there is more blow by gas the air intake system will have to process more blow by gas. Further because of the diminished capacity of the engine to draw in intake air the there is not enough negative pressure to draw the blow-by fuel air mixture into the intake system and some of the fuel air mixture would therefore travel to ambient air.
Still another problem with the introduction of the fuel and air into the intake air supply when the engine is cold is that there will not be adequate flow in the intake member to properly mix the blow by gas with the incoming air. This lack of a proper uniformity of the air with the blow by gas could destroy the uniformity of the charge that is injected into the cylinder resulting in misfiring or diminished engine performance.
In addition, if a crankcase ventilation system is provided, its components may interfere with other engine components and may undesirably increase the size of the engine, and thus, the motor.
An engine arrangement for an engine powering an outboard motor which is compact and reduces the problems associated with the blow-by gas is therefore desired.